I'm doing a "refresh".. mainly we are going responsive so that users over 1366px width will see a large layout with bigger media objects, users below 1366px will see the same layout with a slightly better UI. At what point do you ask users if they want to see the new design? How radical should the difference be? Do you let users decide or is the best way to roll it out in sample sizes?
Update: Here is some advice extracted from the interview (their experience is mostly related to building a SaaS product, so take that into account):